President George Bush is to embark on a multimillion-dollar plan to tackle the powerful Mexican drug cartels who control the flow of most of the cocaine and other illicit drugs into the US.

It would be the biggest US drug offensive since the undeclared war they launched against Colombian drug barons almost 10 years ago.

The aid package, which has been under discussion for months, will top the agenda when Mr Bush meets the Mexican president Felipe Calderón at a North America summit on August 20-21 in Quebec.

The Mexican cartels, who displaced the Colombians as controllers of the trade into the US at the end of the 90s, smuggle the drugs across the long land border, through tunnels and by sea.

The US state department estimates earnings from production and trafficking from Mexico are between $8bn (£4bn) to $25bn a year. Such a lucrative trade has led to inter-cartel wars in Mexico that claimed 2,000 lives last year in execution-style killings and could surpass that total this year, with more than 1,400 so far.

Given historic Mexican suspicion about US interference, US involvement is unlikely to be as direct as it was in Colombia, where US forces mounted helicopter attacks on drug-production centres.

The US has drug enforcement agents based in Mexico but they are not allowed to carry weapons or conduct independent investigations.

The US is expected to offer an aid package providing planes, surveillance equipment, radar and training. There would also be closer cooperation between US and Mexican intelligence agencies.

About 25,000 Mexican troops and special police are battling the cartels, and the US last year provided training for 4,500 of them. The US state department is already funding a surveillance system to help monitor mobile phones and email.

But US help is minimal at present compared to the $5bn spent over the past seven years in Colombia.

Discussions about the US aid are still under way but, because of the sensitivity, there is a reluctance to discuss details. Sean McCormack, the state department spokesman, said: "In as much as it is a problem for both countries, the solution lies both with the US and Mexico. President Calderón has taken a brave and firm stance in fighting these drug cartels. We want to talk to him about how we can support that effort."

Mr Calderón has hinted that the US should provide aid because he sees it as US problem. "We're not asking the US for charity, we're asking them to assume co-responsibility of the situation," Mr Calderón said this year.

The Colombia operation, Plan Colombia, remains contentious, with many in the US Congress claiming it was a fiasco and that the billions spent by the US over the past seven years has been wasted, partly because much of the money was channelled to fighting rebels.

The package would need Congressional approval. Among Congressmen who support it, Henry Cuellar, a Democrat from Texas, said: "We're looking at assistance, technical training and equipment to fight the increasing drug warfare they have."

The Bush administration is not planning to abandon the Colombian operation but sees the financial aid to Mexico as opening up a new front. The danger is that, if successful, the trade would just move elsewhere in Central or South America.

Backstory

Mexico's drug traffickers rose to supremacy following the demise of the Colombian cartels in the 1990s. Mexicans control 90% of the routes into the US market. The main battle is between the Sinaloa cartel (headed by Joaquín "el Chapo" Guzmán) and the Gulf cartel (whose leader Osiel Cárdenas was extradited to the US in January). In June, traffickers sent a warning note to the public security chief in the eastern state of Veracruz accompanied by a severed head.